The midbrain, also known as the mesencephalon, is the middle division of the embryonic brain, which includes the tectum and tegmentum. The midbrain is considered to be part of the brainstem. It is involved in functions such as vision, hearing, eye movement, and body movement. The reticular formation in the midbrain collects input from higher brain centers and passes it to motor neurons. The substantia nigra helps "smooth" out body movements; in Parkinson's disease, this region is damaged.